The present invention relates to an improvement of a linear transportation system for transporting an article without using any transmission mechanism.
FIG. 4 is a perspective view of a conventional linear transportation system which includes a pair of upper parallel guides 1 (only are is shown) and a pair of lower parallel guides 1' (only one is shown). Between the upper and lower guide pairs 1, a linear motor mechanism is arranged. The linear motor mechanism includes a plurality (only two are shown in FIG. 4) of series arranged, flat stationary portions 3 and 3A mounted on the lower guides 1. Primary windings are embedded therein as is well known. The linear motor mechanism further includes a slider 11 as a movable member, which is disposed above the stationary portions 3 and 3A with a constant spacing D therebetween. An article to be transported (not shown) is disposed on the movable member. The slider 11 contains a secondary conductor (not shown) embedded therein. The slider 11 further has a plurality of rollers 2 on opposite edge portions thereof for smoothing its movement along the upper guides 1.
As shown in FIG. 5 which is a block diagram of a driving arrangement for the linear motor mechanism, the stationary portions 3 and 3A are driven by an a.c. power source 4 through a plurality of contacts 5 and 5A which on-off control the a.c. current to be supplied to the primary windings of the stationary portions 3 and 3A.
A plurality of brake mechanisms 6 and 6A are provided for applying braking force to the movable member via the stationary portions 3 and 3A. These brake mechanisms 6 and 6A are selectively energized by a brake power source 7 through a plurality of contacts 8 and 8A.
A controller 9 controls the driving power source 4 and the brake power source 7 according to running instructions which may be preprogrammed or given by an operator. A position sensor 10 is connected to the controller 9 to feed back the position of the slider 11.
The slider 11 is supported by reactive forces produced by the lower guides 1 and driven by a varying magnetic field produced by the stationary portions 3 and 3A therealong. The position of the slider 11 along the guides 1 is detected by the position sensor 10.
As will be clear to those skilled in the art, in order to obtain a stable driving torque in the conventional linear transportation system mentioned above, the gap D between the stationary portions 3 and 3A and the slider 11 has to be always maintained constant. In order to realize this, the guides 1 have to be machined and assembled with high precision, and thus the maintanace and/or regulation of the guides 1 is complicated, time consuming and requires considerable labor.